As use of palletized warehousing expands and the cost of land for and of the building of warehouse facilities increases, the trend has been to use higher and higher storage racks. This conserves floor space. However, it increases the risk of injury to personnel should the articles stored on the pallets for any reason become unstable and fall. This can be the cause of serious, even fatal, injury. This problem can result from slow compression of the lower layers of goods stored on a pallet. This is particularly a risk of articles with low turnover and, therefore, subject to long-term storage. It can also result from small movements of the storage rack due to such causes as exterior traffic, adjacent construction activity or minor earth movements. As a result, the once vertically stacked load with uniform weight distribution becomes unbalanced and inclined to one side. Once this starts, the result can be progressive unbalancing and instability of the load. If this happens to be toward an aisle, the result could be serious to those in the aisle below, should some of the stored articles fall.
Another source of similar problems are pallets storing assorted articles loaded by personnel who are insufficiently trained or careless about arranging the articles on the pallet. Thus, heavy articles may be placed on top of lighter ones, less able to maintain their geometry when under such compressive loads. This type of article storage becomes particularly critical when storage racks become very tall to compensate for lack of adequate floor space. Today, it is not unusual to use racks substantially identical to those previously used but in warehouse facilities in which the pallets are stored in vertical tiers five or more pallets high. Thus, the articles on the upper pallets can fall a substantial distance and generate serious impact force.